"Well, we've tried every device and you still won't talk - every device, that is, except for this little baby we simply call 'Mr. Thingy.'":
OK, perhaps a little more explanation than this obscure Far Side reference is in order. As mentioned before, with top-balanced lithium cells, you need to shut off charging current if any cell hits the high-voltage cutoff point (3.6V in my case). Some chargers have ways to do this with a signal from the BMS. But every charger is different. I may want to change chargers some day, and in fact may want to experiment with an off-board charger for fast charging, so I created Mr. Thingy. All Mr. Thingy does is provide a place to mount:
- A 40-amp solid state AC relay which can turn off the charger in a high-voltage-cutoff event
- The circuit board which handles the J1772 pilot and control signals
- The 12 volt power supply which powers both the relay coil as well as the "I'm plugged in, don't drive away you dummy!" light and interlock
- A kilowatt-hour meter to keep track of electricity used during charging
- Various plugs and receptacles to make switching between J1772 and a regular extension cord, and between the on-board charger and an off-board charger, convenient
All of this in an 8x8x4 inch box! Here is the circuit diagram:
You can find the PDF of this circuit diagram here. And here is the completed enclosure, mounted and attached:
For those who do not want to open the PDF, here is the note from that PDF explaining operation:
If the inlet 10-30P plug “B” is unplugged from the J1772, then the AVC1 will not have ground and will therefore not handshake with the J1772 EVSE, preventing any power from being present on the 10-30R receptacle labelled “A”. This is intentional.
When unplugged from the J1772, the 10-30P plug labelled “B” may be plugged in to a NEMA 10-30R receptacle for direct charging. The on-board charger can be unplugged from the 10-30R receptacle labelled “C” and another charger plugged into it for higher-power BMS-controlled charging.
J1772 Inlet from Tucson EV has the 2.74k ohm resistor preinstalled between PRX and ground.
All high-current 240VAC power wiring is 10 AWG.
EDIT Sep 3 2013: Per this post, this did not quite work initially - the EVSE indicated a "line fault" . Swapping the PRX and PIL lines on the J1772 AVC1 unit fixed the problem! I verified that all the other circuity is installed properly and working - connecting the cell loop (with no cells) causes the charge relay to engage, the 12V power supply is working, and everything seems happy. The circuit diagram for this circuitry has been updated, and now matches this updated PNG: